Didache (Chapter 7)
After you have said these things, baptize in the name of the Father and of the Son and of the Holy Spirit, in flowing water.
Didache 7
Now concerning Baptism, thus shall you baptize: after you have said these things, baptize in the name of the Father and of the Son and of the Holy Spirit, in flowing water. If you do not have flowing water, baptize in other water. And if you are unable to in cold water, then in warm. If you have neither, pour out water upon the head three times in the name of the Father and of the Son and of the Holy Spirit. And before baptizing, let the one baptizing and the one being baptized fast beforehand and some others if they are able. And you shall command the one who is to be baptized to fast for one or two days beforehand.
6th century tapestry of the virgin and Child, surrounded by the twelve apostles [From the Cleveland Museum of Art]
Find Chapters 1–6 here.

